The invention relates to a radiation source assembly for optical transducers used for analysis of media, whereby the radiation source assembly comprises: a first and a second radiation source, of which the second radiation source is transparent for radiation emitted by the first radiation source, and of which the first radiation source is located, in relation to the second radiation source, in such a position that it emits through the second radiation source; a band-stop filter located between the first and the second radiation sources, so that the radiation emitted by the first radiation source passes through it. The invention also relates to a non-dispersive transducer utilizing such a radiation source assembly, whereby the transducer further comprises a radiation detector located to receive the radiation emitted by the first and second radiation sources. Particularly the invention relates to the analysis of gases and gaseous mixtures, although its range of use is not limited to these.